Tooth Eruption

Question 1

What is tooth eruption?

Answer 1

Movement of a tooth:

• from developmental position in jaw
• to its functional position in occlusion in the mouth

'’Eruptive’’ movements continue adjusting tooth

• over-eruption in response to opposing extraction
• compensation for tooth wear

Active eruption: bodily movement of the tooth

Passive eruption: uncovering of the tooth by apical gingival migration

Question 2

What are some pre-eruptive movements?

Answer 2

Pre-eruptive movements:

• during tooth development
• teeth move as jaw grows
• successional teeth move from a lingual/palatal position e.g. lower premolars start lingually and move between the roots of the primary molars
• bone remodelling

Question 3

What are the eruptive movements?

Answer 3

Eruptive movements:

• movement into the mouth and into occlusion
• mainly axial movement
• eruptive force ~5-10g
• variable speed: 1-10 microns per day intraosseous, 75 microns per day supraosseous

Balance between:

• eruptive forces
• resistive forces - overlying tissues

Question 4

What are some eruption theories?

Answer 4

Push forces on the tooth:

• root formation
• bone formation
• fluid pressure

Pulling force:

• PDL: collagen contraction, fibroblast contraction, fibroblast migration

Question 5

What information is there for root formation?

Against?

Answer 5

Root formation:

For - roots normally form during eruption

Against - some teeth have eruption paths >> root lengths

• impacted teeth with fully formed teeth can erupt of impaction released
• experimental evidence: rat incisor, removed root end, tooth continues to erupt

Question 6

Evidence for fluid pressure?

Against?

Answer 6

Hydrostatic pressure: FOR

• periodontal vasculature
• cervical sympathetic stimulation: vasoconstriction, cessation of eruption, reversible on cessation
• sympathectomy: vasodilation - increased tissue pressure, increase eruption rate

Against:

• root resected rodent incisor erupt normally

Question 7

Evidence from the pull - PDL fibres theory?

Answer 7

• disrupt collagen formation: no vitamin C - essential for collagen synthesis

–> slower eruption rate or no change in eruption rate, root formation continues

• teeth erupt when PDL fibres are not well developed

Question 8

Evidence for fibroblast migration/contraction:

Answer 8

For: fibroblast migration/contraction

• fibroblasts show motility when cultered
• fibroblasts move cervically on eruption
• colchiciine - reduces cell motility -> retards eruption

Against:

• PDL fibroblasts dont have organelles for motility
• no evidence that they can exert eruptive force

Question 9

What is tooth eruption least likely to be?

Probably due to?

Answer 9

Likely not due to:

• bone formation
• root formation

Probably due to:

• pull: by PDL fibroblasts
• push: hydrostatic pressure

Question 10

How are primary teeth exfoliated?

What are the post-eruptive movements?

Answer 10

• must be resorbed to facilitate successional eruption
• pressure of tooth on bone –> resorption
• primary teeth resorbed by odontoclasts: multinucleated osteoclast like cells, derived from monocytes

Post-eruptive movements:

• accomodate for growth
• compensate for occlusal wear
• accomodate for approximal wear
• following extraction of opposing teeth